1. Field of the Invention
The present invention relates to a method for recycling metals from waste catalysts, particularly to a method for recycling metals from waste molybdic catalysts by using a highly oxidized acid.
2. Description of the Related Art
In oil-refining industry, catalysts, particular to RDS (residual desulfurization) catalyst and HDS (hydrodesulfurization) catalyst have been widely used in hydro-desulphurization processes. Both of the RDS catalyst and the HDS catalyst have a carrier of alumina, with the carrier of alumina to immobilize metals, for example vanadium, molybdenum or nickel, or metallic oxides on its surfaces. Accordingly, the effects of the RDS catalyst or HDS catalyst are easy to be ineffective due to the contamination and absorption of mass iron or phosphorus during catalysis process. Therefore, a great amount of waste catalysts are generated during the processes of oil-refining, and which may lead to serious pollutions or ecological crisis if a proper treatment of those waste catalysts has not been gone through.
In frankly, the waste catalysts, including waste RDS catalyst and HDS catalyst, are rich in metals, such as molybdenum, nickel, even aluminum obtained from the surfaces of the carrier of alumina, and those metals are capable of being recycled and reused in industries. With such propose, it is a need of providing a method for recycling metals from waste catalysts, for the sake of obtaining a dramatic amount of metals from the waste catalysts and further applying recycled metals in diverse industries.
A conventional technique for recycling metals from waste catalysts as disclosed in China Patent No. CN1557978A and entitled “PRODUCTION TECHNOLOGY FOR EXTRACTING VANADIUM AND MOLYBDENUM FROM SPENT ALUMINUM BASE MOLYBDENUM CATALYZER USING WET METHOD” comprises steps of roasting, by sodium-roasting aluminum base molybdenum catalyzer at 950-1050° C. for 2-3 hours; and leaching, by recycling vanadium and molybdenum from the aluminum base molybdenum catalyzer.
However, a high temperature (more than 950° C.) is needed in the step of roasting of the conventional technique, and therefore it is costly and wasteful in use of energy. Furthermore, sulfur or sulfide in the aluminum base molybdenum catalyzer are easy to diffuse through the processes under the high temperature of the step of roasting, leading to serious contamination and pollutions on air or water resource. Also, nickel in aluminum base molybdenum catalyst is uneasy to be recycled via the sodium-roasting process, so that the efficiency of the conventional technique for recycling metals from waste catalysts is quite low and inconvenient.
Another conventional technique for recycling metals from waste catalyst is disclosed in China Patent No. CN1328396C and entitled “METHOD FOR EXTRACTING VANADIUM, MOLYBDENUM, NICKEL, COBALT, ALUMINUM FROM WASTE ALUMINUM BASE CATALYST,” in which, aluminum catalysts are roasted at 600-900° C. for 0.5-2 hours, soaked in 80-90° C. hot water, and then further soaked in sulfuric acid to recycle nickel and cobalt and to obtain a residue after recycling. Moreover, vanadium and molybdenum can also be recycled from the residue by adding barium hydroxide or barium aluminate into the residue to generate sodium aluminate solution, and sequentially isolating vanadium and molybdenum from the sodium aluminate solution. In this way, the recycling rate of metals in aluminum catalyst will achieve 91%.
Although the conventional technique above can effectively recycled metals from aluminum catalyst, sulfur or sulfide in aluminum catalyst will still remain in the aluminum catalysts and result in contamination and pollutions on air or water resource. Moreover, an additional oxidization of vanadium and molybdenum is needed for extracting vanadium and molybdenum from the aluminum catalysts, and however, the oxidization of vanadium and molybdenum may increase the impurity thereof and diminish the recycling rate of vanadium and molybdenum as well.
Additionally, there is a great amount of aluminum remained in the aluminum catalysts, with the result in interfering with the recycling of vanadium, nickel and molybdenum from the aluminum catalysts. In conventional arts, aluminum in the aluminum catalysts are additionally recycled by aerating carbon dioxide into the sodium aluminate solution, followed by roasting the sodium aluminate solution at a high temperature to obtain alumina. In this situation, the recycled metals only can be obtained in a time-and-cost consuming process, with poor quality and low recycling rate. It is suggested that, the conventional techniques has plenty of disadvantages and inconvenience, and therefore there is an urgent need of improving the conventional technique for recycling metals from waste catalysts.